Experimental device-independent verification of quantum steering

TL;DR

This paper demonstrates a new device-independent method to verify quantum steering, enabling secure quantum communication without trusting measurement devices, even when Bell nonlocality is absent.

Contribution

It introduces device-independent steering protocols that do not require trust in measurement devices, expanding secure quantum communication possibilities.

Findings

Successfully verified quantum steering device-independently for singlet states.

Demonstrated verification even when Bell inequalities are not violated.

Experimental validation of protocols with high robustness to losses.

Abstract

Bell nonlocality between distant quantum systems---i.e., joint correlations which violate a Bell inequality---can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols for quantum information tasks such as cryptographic key distribution. However, complete verification of Bell nonlocality requires high detection efficiencies, and is not robust to the typical transmission losses that occur in long distance applications. In contrast, quantum steering, a weaker form of quantum correlation, can be verified for arbitrarily low detection efficiencies and high losses. The cost is that current steering-verification protocols require complete trust in one of the measurement devices and its operator, allowing only one-sided secure key distribution. We present device-independent steering protocols that remove this need for trust, even when Bell nonlocality is not present. We experimentally demonstrate this principle for singlet states and states that do not violate a Bell inequality.